The aims of this research project are 1) to investigate systematically how diagnoses of color deficiency are influenced by test-stimulus duration, 2) to account for observed individual differences in susceptibility to adaptation within a theoretical framework for understanding normal and deficient color vision, and 3) to relate individual differences in adaptation processes to differences in settings of unique-hue spectral loci among observers with normal color vision. During the current project period, a large number of observers are being screened with a set of standard color-vision tests, including an anomaloscope for which test field exposures are controlled at either 0.5 or 5 sec. A subset of these observers is also being tested systematically on the anomaloscope with a range of exposure durations from 50 msec to 10 sec to isolate groups of individuals with characteristically different patterns of adaptation. The data which have been collected indicate that for observers with normal color vision and for those diagnosed as color deficient there is a loss of discrimination as the exposure duration of the sitimulus increases from 200-500 msec to 10 sec. For most of the deutan and protan observers there is also a loss of discrimination at exposure durations shorter than 200 msec. A notable finding is that some observers who are diagnosed as dichromats at durations of 5 or 10 sec are capable of trichromatic matches at shorter exposures. There are considerable differences in the rate of change in discrimination as a function of duration among the observers and presumably in the rates of adaptation of their color-vision systems.